New To this – Need some help uploading new view

Hi,

I am new to this and have hosting with Ultra Website Hosting they do allow ones to uplaid wordpress by use of the Fantastico De Luex program… I have it up in running but I would like to change the view of it. when i have logged in to my word press and
go to dashboard and go to
change your theme completely,
I then go to Install Themes TAB,
I then go to UPLOAD
hERE IT SAYS TO INSTALL A THEME IN .ZIP FORMAT….
when I browse and go to my folder where the new theme is It won’t let me install anything?

Question 2
I want to have move then one wordpress going so
A) should i put each one in the a sub domain
or
B) should can i put them all in the rout directory
Can someone please help me.
??